Relationship between drone compass and device compass

[JOHNVOSS]

I frequently see posts that stress the importance of insuring that the drone is not near ferrous metal when starting up so that the drone compass will not be affected. Secondly, it is important to insure that the compass on the device displays the same direction that the drone is pointed. I have 2 questions.
1.What is the relationship between the 2 compasses?
2. If the drone has been safely positioned for takeoff but the device compass needs calibration and/or is in proximity to metal would it still be able to show the direction that the drone is pointed?

Thanks.

 

[Ty Pilot]

This is an excellent post called: A Short Explanation Of Compass Function, Calibration And Errors

If you really what to understand how the compass in a modern drone works, how it can fail, what can cause it to fail and what happens when it fails - read that post I linked too.

Your two questions indicate that you may be misinterpreting what you are reading. The device compass? All that matters is that when you place your drone for takeoff - IT's compass must not be near ferrous material. If it is, the drone's false compass' reading, will show up on the screen (device) and it is up to the pilot to check that the direction the drone is indicating, is in fact how it is oriented. If not then you need to move to a new location. Calibrations of the drone or device have nothing to do with this.

When people refer to the 'compass' on the device screen, they are referring to the map and the orientation of the little icon representing your drone. It is the drone's compass reading however; that is being displayed and it is up to the pilot to recognize any misalignment and move the takeoff location until the drones compass is displayed as true.

 

[slup]

Think you slightly have misunderstood what you've read...

It's correct that it's of greatest importance that the drone compass isn't magnetically disturbed during booting up the drone... as it's just there in the very beginning of the power on the IMU reads off the cardinal direction from the compass. If the compass is disturbed when this happens the IMU will be wrongly initialized & the drone will not have correct information about which direction the drone is pointing... this will be disastrous once the drone tries to hold position when for instance affected by wind. The FC will, as the drones direction information is false, activate the wrong motors & instead of closing the growing positional error due to the wind drift... the positional error instead grows. This rapidly goes out of control & the drone flies away.

And it's here below you've probably have a slight misunderstanding...

In order to verify that the IMU initialization went as it should when the drone was powered on & the drone have the correct information about in which direction it points, before you go airborne... you,

...bring up the map view in the app, there you check so the drone icon (an arrow) points equal to other map objects like houses & roads and such... as the drone does in reality. So for instance... if your drone in reality have a house in front of it, the drone icon on the map should have that also. If the drone icon on the map says that the house is on the side or behind the drone that's wrong... the IMU initialization failed when the drone was powered up, most probably due to that something disturbed the compass at that moment. You need here power down the drone... move away to another power on spot & repeat everything until the reality & info on the map matches.

Then the mobile device compass you asked about...

You don't need a device with a built in compass for a safe flight... the compass there serves mainly 2 purposes.

1. It will rotate the map view so the view lines up with reality if you set it to do that... you can also chose to deactivate the map rotation & instead always have the maps north towards the top of the screen. So this have nothing to do with what I explained earlier.

2. A mobile device compass will also make it easier for you to know in which direction relative how you're turned, the drone is far out there in the sky... this so you know in which direction you should point the RC antennas for the best connection. (The tool for this is the larger "radar" icon in the lower left corner in the app.)

 

[mobilehomer]

Another point for you, the phone compass sometimes needs to be synced to the app. The dot w/arrow on the attitude indicator SHOULD point to the drone icon. If not, do the spin-it-around figure 8 moves with the device until it gets satisfactory. I have to do this with my RC Pro on occassion, it does get more accurate the longer it stays on.

 

[JOHNVOSS]

When people refer to the 'compass' on the device screen, they are referring to the map and the orientation of the little icon representing your drone. It is the drone's compass reading however; that is being displayed and it is up to the pilot to recognize any misalignment and move the takeoff location until the drones compass is displayed as true.

Back in the mini 1 days there were many discussions about how the metal in the controller was affecting the phone compass and as others found turning the phone around in the controller helped but I could never get the arrow on the screen to equal the direction of the drone. Now with the Mini2 in map view the direction on the screen compared to drone direction is frequently off by a noticeable amount even after calibrating the phone. How can that be if the compass direction on the phone is the direction of the drone?

 

[slup]

...Now with the Mini2 in map view the direction on the screen compared to drone direction is frequently off by a noticeable amount even after calibrating the phone. How can that be if the compass direction on the phone is the direction of the drone?

The phone compass & how the map is turned is totally irrelevant when it comes to detect if you have a failed IMU initialization (having a sk. yaw error).

What matters is how the drone icon (on the map) is turned in relation to other objects in the map... & if the drone in reality is turned in the same way in relation to those same real objects.

To the left the reality ... the drone is pointing at the house.

To the right ... the app with the map view, the arrow like drone icon is pointing towards the house. (even though I've drawn the map itself a bit turned clockwise)

All is good here... icon on the map points equal to reality.

 

[JOHNVOSS]

Thank you. I will check that out next week.

 

[Ralph thompson]

You don't mention which drone or controller but the Smart Controller and RC Pro have an internal compass that also needs to be occasionally calibrated (p19 in the RC Pro manual).
The drone compass & the Smart/RC Pro compass operate independently so they both need to be calibrated and unaffected by magnetic interference to function correctly and for the drone to appear in the correct place and orientation on the map. Fortunately you should get a message if they're not calibrated.

 

[slup]

You don't mention which drone or controller but the Smart Controller and RC Pro have an internal compass that also needs to be occasionally calibrated (p19 in the RC Pro manual).
The drone compass & the Smart/RC Pro compass operate independently so they both need to be calibrated and unaffected by magnetic interference to function correctly and for the drone to appear in the correct place and orientation on the map. Fortunately you should get a message if they're not calibrated.

In post #5 it seems to be a Mini 2 & he refers to a "Phone" ... so definitely a phone as a screen device.

But no matter if it's a SC, a RC Pro or a phone... the screen device compass is totally irrelevant when it comes to yaw errors... it only affect certain non flight critical screen device functions.

 

[Ralph thompson]

 

[JOHNVOSS]

Thanks for all your responses.
I'm trying to keep this simple. Richard, in your picture, that situation gives the appearance of an error which has been discussed frequently here, particularly with the M and M2. Would it be safe to say that, assuming that the drone imu and compass are correct, the orientation of the map on the device is causing this. In other words, the phone (in my case) and the drone compasses do not agree on the direction of North.

John

 

[slup]

I'm not a Richard, that was only a guy that "liked" my drawing skills

But anyway...

If you stood behind the drone in the left "reality part", turned towards the house with your controller in front of you pointing the antennas towards the house, but the "right app part" looked like I have drawn it, that would mean that your phone compass is deflected due to some reason (might be something in the controller that deflects it or something else like a phone cover with a magnetic closure) a calibration of the phone compass with the phone still attached to the controller might fix it (if the deflection is due to interference from the controller).

The "right app part" would be correct (and the phone compass would be correct) if you with the controller was turned about 45 degrees CCW away from facing the house...

What matters in order to avoid a yaw error causing a flyaway at height is that the blue arrow I've drawn points equal in relation to objects... on the app map & in reality.

 

[JOHNVOSS]

Thanks. That basically confirms what I'm saying. I'm surprised I never saw that detailed an explanation amidst the numerous posts about this issue. Yes, there were comments about phone calibration in the controller but I never saw anything about pointing at an object. Thanks again.